The overall goal is to obtain a better understanding of the processes whereby chronic exposure to supraphysiologic concentrations of glucose can severely compromise pancreatic islet insulin gene expression. The four specific aims are: (1) to ascertain whether the adverse consequences on insulin gene expression caused by chronically culturing B-cell lines in media containing supraphysiologic glucose concentrations reflects a completely linear or a threshold effect of glucose concentration; (2) to determine whether the adverse effects of chronically culturing B-cell lines in media containing supraphysiologic glucose concentrations can be prevented by including somatostatin in the media to distinguish "beta-cell exhaustion" in the function sense from glucose toxicity in the chemical sense; (3) to determine whether restoration of defective gene expression of transcription factors such as STF-1 and 3b1, which promote insulin gene expression, will correct the adverse effects caused by chronic exposure of B-cells to supraphysiologic glucose concentrations; and (4) to determine whether prolonged hyperglycemia in Zucker diabetic fatty rats induces defective insulin gene expression in isolated islets. The methods used to achieve the specific aims will involve studies of static and phasic hormone secretion; measurement of cellular hormone content and mRNA levels; studies of insulin gene and STF-1 gene transcription by CAT reporter experiments; and reconstitution of cells with expression vectors for STF-1 and 3b1 genes. A common feature of these experiments involves prolonged passaging of various cell lines for 6-12 months to assess the adverse effects of chronic exposure to supraphysiologic glucose concentration on gene expression of insulin and insulin gene transcription factors. The long term goal is to establish mechanisms for glucose toxicity of the pancreatic beta cell.